Aviation and Flying Questions That You Have Been Dying To Ask And Want To Know

N918KT

N918KT

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KT
Hey, thought I start a thread where people can post questions related to flying and aviation that they have been dying to ask and want to know more about and other people on this forum could answer some of their questions.

I have a few questions that I want to ask you guys to start off.

1. In high-wing airplanes there is a left, right, and both fuel selector knob but in low-wing airplanes there is only a left and right fuel selector knob. Why is there no "both" setting in the fuel selector knob for low-wing airplanes?

2. Do multi-engine piston or twin-engine piston airplanes do their engine runups just before takeoffs like single-engine piston airplanes do and if so how do multi-engine piston airplanes do their runups?
 
N918KT said:
2. Do multi-engine piston or twin-engine piston airplanes do their engine runups just before takeoffs like single-engine piston airplanes do and if so how do multi-engine piston airplanes do their runups?
Click to expand...

Yes, multi-engine pistons do run ups just like singles. Turboprops on the other hand do not.

For most light twins, the big difference over singles is that you have twice the stuff to check so the runup takes a little longer and in addition to cycling the prop, you check the feathering mechanism.

In bigger ME airplanes, we sometimes do the runup on the active runway prior to takeoff. Primary reason for that is the size of the aircraft and the amount of prop blast. You don't want to be sitting in a 172 on the taxiway behind a DC-3 while we are running up.
 
N918KT said:
1. In high-wing airplanes there is a left, right, and both fuel selector knob but in low-wing airplanes there is only a left and right fuel selector knob. Why is there no "both" setting in the fuel selector knob for low-wing airplanes?
Click to expand...

My high-wing aircraft doesn't have a fuel selector knob. Just on or off.
 
N918KT said:
1. In high-wing airplanes there is a left, right, and both fuel selector knob but in low-wing airplanes there is only a left and right fuel selector knob. Why is there no "both" setting in the fuel selector knob for low-wing airplanes?
Click to expand...

Because high-wing airplanes can use gravity to make the fuel flow. Take two glasses. Fill one with water, and simultaneously pour them over your head. You'll get wet.

Low-wing planes have to either push or suck it out of the tank. Most have pumps located in the engine compartments that suck the fuel from the tanks. Take your two glasses, refill one with water, and set them side-by-side on the table. Stick a straw in both glasses, and suck on the two straws simultenously. You'll get mostly air.

Ron Wanttaja
 
Fearless Tower said:
And some do not have a 'both' option.

I can say that I don't think I've seen a low wing airplane with a 'both' selector .
Click to expand...

Never flown a certified low wing with both but a lot of homebuilts have it. My Velocity feeds from both into a 5 gallon feeder tank.
 
N918KT said:
Hey, thought I start a thread where people can post questions related to flying and aviation that they have been dying to ask and want to know more about and other people on this forum could answer some of their questions.

I have a few questions that I want to ask you guys to start off.

1. In high-wing airplanes there is a left, right, and both fuel selector knob but in low-wing airplanes there is only a left and right fuel selector knob. Why is there no "both" setting in the fuel selector knob for low-wing airplanes?

I'm not sure that is true. There are a lot of low wing airliners that have left, center, right, forward aux, rear aux and crossfeed switches for all tanks for all engines.

2. Do multi-engine piston or twin-engine piston airplanes do their engine runups just before takeoffs like single-engine piston airplanes do and if so how do multi-engine piston airplanes do their runups?
Click to expand...

One engine at a time just like every one else.
 
Mason said:
One engine at a time just like every one else.
Click to expand...

That tends to be a matter of personal preference. I like to do one at a time, but I know a lot of guys who will do things like cycle both props together.
 
Mason said:
One engine at a time just like every one else.
Click to expand...

Hey Mason, sorry I don't think I made my question clear, I specifically want to know why low-wing single engine piston airplanes usually do not have a "both" setting in the fuel selector knob.
 
N918KT said:
Hey Mason, sorry I don't think I made my question clear, I specifically want to know why low-wing single engine piston airplanes usually do not have a "both" setting in the fuel selector knob.
Click to expand...

He was responding to your second question about multi-engine runups.
 
Fearless Tower said:
He was responding to your second question about multi-engine runups.
Click to expand...

But I thought Mason was answering my first question since he quoted me and put his answer in the quote box highlighted in blue for the first question.

Edit, yes he was answering my 2nd question but I think he also answered my first question in the quote box.
 
Fearless Tower said:
And some do not have a 'both' option.

I can say that I don't think I've seen a low wing airplane with a 'both' selector .
Click to expand...

I've got one - of sorts.

I have a selector for the left two tanks (aux-main-off), and a selector for the right two tanks (aux-main-off). So I often run a "both" setting. I fact I can run all of the following combinations:

L Tip - R OFF
L Tip + R Main
L Tip + R Tip
L Main R OFF
L Main + R main
L Main + R Tip
R Main L OFF
R Tip L OFF
and of course - OFF-OFF
 
Last edited:
Turboprops often will do a run up on the first flight of the day. No mag check but there are other checks for things like auto feather or NTS.
 
Velocity173 said:
Never flown a certified low wing with both but a lot of homebuilts have it.
Click to expand...

Can you name one? I can't. Certainly not the RV series, and certainly not any well designed low wing airplane that doesn't feed into a sump tank or header tank first (I think some of the Russian types - Yak's and Nanchangs use that approach).
 
Fuel selector on my aircraft on or off. On my light twin run up was just two of everything to check.
 
J35 through M35 Bonanzas had separate "left" and "right" fuel selector positions for the main tanks, but the lone "aux" position caused fuel to draw from aux tanks in both wings simultaneously.
 
kyleb said:
Can you name one? I can't. Certainly not the RV series, and certainly not any well designed low wing airplane that doesn't feed into a sump tank or header tank first (I think some of the Russian types - Yak's and Nanchangs use that approach).
Click to expand...

Well Velocity for one. I imagine the other Rutan canards use both sides at once as well. My Glasair has both as well. Not like it's something dangerous. So it feeds both at once instead of left or right. Unless you fly completely out off trim its a non issue.
 
Velocity173 said:
Well Velocity for one. I imagine the other Rutan canards use both sides at once as well. My Glasair has both as well. Not like it's something dangerous. So it feeds both at once instead of left or right. Unless you fly completely out off trim its a non issue.
Click to expand...

Not correct. If you hook up the tanks in parallel, they won't feed at the same rate. One will have a shorter pick-up tube, one will have a vent that flows more freely. Whatever. That tank will empty faster and eventually run dry first. Then the fuel system will suck air and the prop will stop, even though the other tank contains fuel (maybe a lot of fuel). That makes for an embarrassing day, so well designed aircraft don't do it that way.

Does your fuel system have a sump? From the Velocity XL manual:
The fuel system consists of two 33 gallon wing tanks. There is​
no provision for cross feed as fuel is used from both tanks simultaneously.​
A 4 gallon fuel sump is located behind the rear seat to​
assure fuel supply to the engine in normal flight attitudes. Each​
main tank and sump tank is vented. A mechanical engine-driven​
fuel pump transfers fuel from the sump to the injector...

​
So *that* airplane has a both selection, but the fuel feeds from the tanks to the sump, then to the engine to make sure the engine doesn't suck air like would eventually happen if the engine was fed from "Both" tanks.
 
kyleb said:
Not correct. If you hook up the tanks in parallel, they won't feed at the same rate. One will have a shorter pick-up tube, one will have a vent that flows more freely. Whatever. That tank will empty faster and eventually run dry first. Then the fuel system will suck air and the prop will stop, even though the other tank contains fuel (maybe a lot of fuel). That makes for an embarrassing day, so well designed aircraft don't do it that way.

Does your fuel system have a sump? From the Velocity XL manual:


The fuel system consists of two 33 gallon wing tanks. There is​

​

no provision for cross feed as fuel is used from both tanks simultaneously.​


A 4 gallon fuel sump is located behind the rear seat to​


assure fuel supply to the engine in normal flight attitudes. Each​


main tank and sump tank is vented. A mechanical engine-driven​

fuel pump transfers fuel from the sump to the injector...

​
So *that* airplane has a both selection, but the fuel feeds from the tanks to the sump, then to the engine to make sure the engine doesn't suck air like would eventually happen if the engine was fed from "Both" tanks.
Click to expand...

Yes it has a sump. Didn't say it didn't. Simply saying there is no left or right selection.
 
kyleb said:
Read post 15 in the thread. Which you proceeded to disagree with.
Click to expand...

I don't care about your post. My response was to Fearless. It has nothing to do with having a sump. My aircraft feeds from both tanks and doesn't allow left or right. End of story.
 
ok my question is...

Why don't we normally have a reserve selection on our fuel tanks?
could be similar to how many motorcycles have a reserve selector.
Or simply a small reserve fuel tank.

Brian
 
brcase said:
ok my question is...

Why don't we normally have a reserve selection on our fuel tanks?
could be similar to how many motorcycles have a reserve selector.
Or simply a small reserve fuel tank.

Brian
Click to expand...

Why don't we have one on our car?
 
Geico266 said:
I want to know how an air plane flies. Screw the fuel selector thingy. ;)
Click to expand...

I asked a student once how a rotor system produces lift. "Well...it's like on the discovery channel, it says it beats the air into submission." When he realized I wasn't joking he came up with "It's like a ceiling fan, it takes the air and it pushes it down. It takes the air (lots of hand gestures) and blows it down." He was serious too. A year of flight school and roughly 1 millions dollars and that's what he learned.
 
Geico266 said:
I want to know how an air plane flies. Screw the fuel selector thingy. ;)
Click to expand...

It's simple really.
How_Planes_Fly__Medium_.jpg
 
EdFred said:
Why don't we have one on our car?
Click to expand...

Many do.

A dual pump system is common in fuel injection, and the second stage pump often has a reservoir, kept completely full by the first stage until the tank is totally dry. It's 1 liter on my VW. The Ford that preceded it was much smaller,

The Saturn has a low fuel light and only one high pressure pump in the tank.

The point is to prevent the engine from quitting on hard corners when nearly empty. That would be a big problem with an automatic transmission and power steering, a common combination.
 
MAKG1 said:
Many do.

A dual pump system is common in fuel injection, and the second stage pump often has a reservoir, kept completely full by the first stage until the tank is totally dry. It's 1 liter on my VW. The Ford that preceded it was much smaller,

The Saturn has a low fuel light and only one high pressure pump in the tank.

The point is to prevent the engine from quitting on hard corners when nearly empty. That would be a big problem with an automatic transmission and power steering, a common combination.
Click to expand...

I must not be able to find the lever that switches the tank from ON fuel to RESERVE fuel like I have on my motorcycle. I should probably keep looking for it.
 
brcase said:
ok my question is...

Why don't we normally have a reserve selection on our fuel tanks?
could be similar to how many motorcycles have a reserve selector.
Or simply a small reserve fuel tank.
Click to expand...

Well, 'cuz ya don't want the engine to quit when you run out of non-reserve, and then quit again when you run out entirely. Quitting once is plenty! ;)
 
EdFred said:
I must not be able to find the lever that switches the tank from ON fuel to RESERVE fuel like I have on my motorcycle. I should probably keep looking for it.
Click to expand...

Geez, how old is your bike? Mine is 12 years old and doesn't have a selector. I thought mine was ancient.
 
kyleb said:
Can you name one? I can't. Certainly not the RV series, and certainly not any well designed low wing airplane that doesn't feed into a sump tank or header tank first (I think some of the Russian types - Yak's and Nanchangs use that approach).
Click to expand...

The S-LSA I fly has a both setting but I never use it for reasons discussed prior.

http://www.theairplanefactory.com <-Plane I fly
 
Fearless Tower said:
I can say that I don't think I've seen a low wing airplane with a 'both' selector .
Click to expand...
The Commanders have a "BOTH" position, but they're really a mid-wing with the wing tanks above the carb, not a low-wing with the tanks below, even if they look mostly like a low-wing. The low-wing Globe Swifts also have a one-feed system with a crossfeed between the tanks.

And I would still consider that "ON/OFF" valve in something like a Cessna 150 a "fuel selector" which allows you to select "fuel ON" or "fuel OFF". :wink2:
 
Fearless Tower said:
That tends to be a matter of personal preference. I like to do one at a time, but I know a lot of guys who will do things like cycle both props together.
Click to expand...
I think more twin pilots do the mags together than props, but it's technique, not procedure, so you can do it any way you want. I also think that a simultaneous run-up is the choice for more experienced ME pilots, and you won't see it much during initial ME training or practical tests.
 
brcase said:
Why don't we normally have a reserve selection on our fuel tanks?
could be similar to how many motorcycles have a reserve selector.
Or simply a small reserve fuel tank.
Click to expand...
Complexity issues, which means cost, maintenance, weight, and pilot errors.
 
KT, you do know you don't need a thread for that. It's actually the purpose of the entire board. Posting a separate thread for each question generates more responses and helps keep track of them infinitely better.
 
kyleb said:
Does your fuel system have a sump? From the Velocity XL manual:
The fuel system consists of two 33 gallon wing tanks. There is​
no provision for cross feed as fuel is used from both tanks simultaneously.​
A 4 gallon fuel sump is located behind the rear seat to​
assure fuel supply to the engine in normal flight attitudes. Each​
main tank and sump tank is vented. A mechanical engine-driven​
fuel pump transfers fuel from the sump to the injector...

​
So *that* airplane has a both selection, but the fuel feeds from the tanks to the sump, then to the engine to make sure the engine doesn't suck air like would eventually happen if the engine was fed from "Both" tanks.
Click to expand...

I have never flown a plane with a fuel sump. Just to get this straight in my head, in this type of a fuel delivery scheme, the fuel flows by gravity from the left and right tanks down to a sump located lower than the mains and then the fuel is pumped up to the engine from the sump? Do I have that right?
 
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